reiserfs: Initialize sec->length in reiserfs_security_init().

syzbot is reporting that sec->length is not initialized.

Since security_inode_init_security() returns 0 when initxattrs is provided
but call_int_hook(inode_init_security) returned -EOPNOTSUPP, control will
reach to "if (sec->length && ...) {" without initializing sec->length.
Reported-by: syzbot <syzbot+00a3779539a23cbee38c@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=00a3779539a23cbee38cSigned-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 52ca4b64 ("reiserfs: Switch to security_inode_init_security()")
Signed-off-by: Paul Moore <paul@paul-moore.com>

fs/reiserfs/xattr_security.c

@@ -67,6 +67,7 @@ int reiserfs_security_init(struct inode *dir, struct inode *inode,
 
 	sec->name = NULL;
 	sec->value = NULL;
+	sec->length = 0;
 
 	/* Don't add selinux attributes on xattrs - they'll never get used */
 	if (IS_PRIVATE(dir))